1. Field of the Invention
The present invention relates generally to a communication system for communicating channel quality information (CQI) (e.g., a base station/BS).
2. Description of the Related Art
The Institute of Electrical and Electronics Engineers (IEEE) 802.16e communication system is a communication system employing an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme to support a broadband transmission network for physical channels of the wireless MAN system. While the IEEE 802.16e communication system is discussed in detail along with its problems, similar problems may also arise in other communication systems including but not limited to Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) systems, and the present invention may be applied in any one of those communication systems.
With reference to FIG. 1, a description will now be made of a configuration of the IEEE 802.16e communication system.
FIG. 1 is a diagram schematically illustrating a configuration of a general IEEE 802.16e communication system.
Referring to FIG. 1, the IEEE 802.16e communication system has a multi-cell configuration, i.e., has multiple cells of a cell 100 and a cell 150. The multi-cell configuration includes a base station (BS) 110 for managing the cell 100, a BS 140 for managing the cell 150, and a plurality of mobile stations (MSs) 111, 113, 130, 151 and 153. Signal exchange between the BSs 110 and 140 and the MSs 111, 113, 130, 151 and 153 is achieved using the OFDM/OFDMA scheme. Among the MSs 111, 113, 130, 151 and 153, the MS 130 is located in a boundary, i.e., handover region, between the cell 100 and the cell 150. That is, if the MS 130 moves to the cell 150 managed by the BS 140 in the course of exchanging signals with the BS 110, its serving BS is changed from the BS 110 to the BS 140.
In the IEEE 802.16e communication system, various schemes are being used to support high-speed data transmission, and the typical scheme is an Adaptive Modulation and Coding (AMC) scheme. The AMC scheme represents a data transmission scheme for determining different modulation schemes and coding schemes according to channel conditions between a cell, i.e., BS, and an MS, thereby improving the efficiency of the cell. The AMC scheme has a plurality of modulation schemes and a plurality of coding schemes, and modulates and codes channel signals using the most preferred combination of the modulation schemes and the coding schemes. Each of the combinations of the modulation schemes and the coding schemes is called Modulation and Coding Scheme (MCS), and MCS level 1 through MCS level N can be defined according to the number of the possible MCSs. That is, the AMC scheme adaptively determines an MCS level according to the channel conditions between a BS and an MS currently connected to the BS, thereby improving the full efficiency of the BS system.
In the IEEE 802.16e communication system, in order to use various schemes for high-speed data transmission such as the AMC scheme, an MS must feed back channel state information, i.e., channel quality information (CQI), of a downlink to its BS, i.e., serving BS. With reference to FIG. 2, a description will now be made of a CQI channel configuration for feeding back the CQI to the BS in the IEEE 802.16e communication system.
FIG. 2 is a diagram schematically illustrating a CQI channel configuration for a general IEEE 802.16e communication system.
Before a description of FIG. 2 is given, it should be noted that in the IEEE 802.16e communication system, one CQI channel can include a predetermined number of tiles, for example, 6 tiles. Each tile can include a predetermined number of adjacent data sub-carriers (or sub-carrier bands) for a period of a predetermined number of OFDM symbols. Referring to FIG. 2, when the IEEE 802.16e communication system uses an Optional Partial Usage of Sub-Channels (O-PUSC) scheme, one tile 200 may include eight adjacent data sub-carriers and one pilot sub-carrier for a 3-OFDM symbol period.
Unlike this, when the IEEE 802.16e communication system uses a Partial Usage of Sub-Channels (PUSC) scheme, one tile 250 may include eight adjacent data sub-carriers and four pilot sub-carriers for a 3-OFDM symbol period. With reference to FIG. 3, a description will now be made of a tile format for the O-PUSC scheme and a tile format for the PUSC scheme.
FIG. 3 is a diagram schematically illustrating a tile format for the O-PUSC scheme and a tile format for the PUSC scheme.
Referring to FIG. 3, as described above in connection with FIG. 2, a tile 200 for the O-PUSC scheme and a tile 250 for the PUSC scheme can each include a total of eight data sub-carriers Mn,8m through Mn,8m+7 for a 3-OFDM symbol period. Herein, n denotes a CQI channel index and m denotes a tile index. Therefore, Mn,8m through Mn,8+7 represent eight data sub-carriers constituting an mth tile of an nth CQI channel. In addition, as described in connection with FIG. 2, the tile 200 for the O-PUSC scheme includes one pilot sub-carrier and the tile 250 for the PUSC scheme includes four pilot sub-carriers.
Next, a description will be made of an operation of transmitting CQI from an MS to a BS over a CQI channel in the IEEE 802.16e communication system.
A BS may transmit, to an MS, information (e.g., a CQI channel index) on a CQI channel allocated to the MS through a CQI channel allocation message. Upon receiving the CQI channel allocation message, the MS may detect an index of the CQI channel allocated thereto, generate its downlink CQI with a predetermined number of, for example, 6 bits, and feed back the generated CQI to the BS over the allocated CQI channel. A description will now be made of an operation of feeding back of the CQI from the MS to the BS over the CQI channel.
A Quadrature Phase Shift Keying (QPSK) signal that the MS must transmit through each of data sub-carriers constituting each tile of the CQI channel according the generated CQI may be generated through the following two steps.
A first step determines a modulation vector sequence that is mapped to the 6-bit CQI on an one-to-one basis (i.e., each CQI bit value is mapped to an individual modulation vector sequence).
That is, the first step determines modulation vector sequences that are individually mapped to 6 possible bits for generation of the CQI, and the modulation vector sequences individually mapped to the 6 possible bits for generation of the CQI are shown in Table 1A through Table 1D.
TABLE 1AModulation vector sequence6 bit CQI(tile #0), (tile #1), (tile #2), (tile #3), (tile #4), (tile #5)0b0000000, 0, 0, 0, 0, 00b0000011, 1, 1, 1, 1, 10b0000102, 2, 2, 2, 2, 20b0000113, 3, 3, 3, 3, 30b0001004, 4, 4, 4, 4, 40b0001015, 5, 5, 5, 5, 50b0001106, 6, 6, 6, 6, 60b0001117, 7, 7, 7, 7, 70b0010002, 4, 3, 6, 7, 50b0010013, 5, 2, 7, 6, 40b0010100, 6, 1, 4, 5, 70b0010111, 7, 0, 5, 4, 60b0011006, 0, 7, 2, 3, 10b0011017, 1, 6, 3, 2, 00b0011104, 2, 5, 0, 1, 30b0011115, 3, 4, 1, 0, 2
TABLE 1BModulation vector sequence6 bit CQI(tile #0), (tile #1), (tile #2), (tile #3), (tile #4), (tile #5)0b0100004, 3, 6, 7, 5, 10b0100015, 2, 7, 6, 4, 00b0100106, 1, 4, 5, 7, 30b0100117, 0, 5, 4, 6, 20b0101000, 7, 2, 3, 1, 50b0101011, 6, 3, 2, 0, 40b0101102, 5, 0, 1, 3, 70b0101113, 4, 1, 0, 2, 60b0110003, 6, 7, 5, 1, 20b0110012, 7, 6, 4, 0, 30b0110101, 4, 5, 7, 3, 00b0110110, 5, 4, 6, 2, 10b0111007, 2, 3, 1, 5, 60b0111016, 3, 2, 0, 4, 70b0111105, 0, 1, 3, 7, 40b0111114, 1, 0, 2, 6, 5
TABLE 1CModulation vector sequence6 bit CQI(tile #0), (tile #1), (tile #2), (tile #3), (tile #4), (tile #5)0b1000006, 7, 5, 1, 2, 40b1000017, 6, 4, 0, 3, 50b1000104, 5, 7, 3, 0, 60b1000115, 4, 6, 2, 1, 70b1001002, 3, 1, 5, 6, 00b1001013, 2, 0, 4, 7, 10b1001100, 1, 3, 7, 4, 20b1001111, 0, 2, 6, 5, 30b1010007, 5, 1, 2, 4, 30b1010016, 4, 0, 3, 5, 20b1010105, 7, 3, 0, 6, 10b1010114, 6, 2, 1, 7, 00b1011003, 1, 5, 6, 0, 70b1011012, 0, 4, 7, 1, 60b1011101, 3, 7, 4, 2, 50b1011110, 2, 6, 5, 3, 4
TABLE 1DModulation vector sequence6 bit CQI(tile #0), (tile #1), (tile #2), (tile #3), (tile #4), (tile #5)0b1100005, 1, 2, 4, 3, 60b1100014, 0, 3, 5, 2, 70b1100107, 3, 0, 6, 1, 40b1100116, 2, 1, 7, 0, 50b1101001, 5, 6, 0, 7, 20b1101010, 4, 7, 1, 6, 30b1101103, 7, 4, 2, 5, 00b1101112, 6, 5, 3, 4, 10b1110001, 2, 4, 3, 6, 70b1110010, 3, 5, 2, 7, 60b1110103, 0, 6, 1, 4, 50b1110112, 1, 7, 0, 5, 40b1111005, 6, 0, 7, 2, 30b1111014, 7, 1, 6, 3, 20b1111107, 4, 2, 5, 0, 10b1111116, 5, 3, 4, 1, 0
The modulation vector sequences individually mapped to the 6 possible bits for generation of the CQI on an one-to-one basis (i.e., each CQI bit value/combination is mapped to an individual modulation vector sequence) are determined as shown in Table 1A through Table 1D. For example, for a 6-bit CQI of 0b 001001, modulation vector sequences for representing the 6-bit CQI of 0b 001001 become {3,5,2,7,6,4}. Herein, the modulation vector sequences {3,5,2,7,6,4} mean that they are mapped to 6 tiles constituting the CQI channel on an one-to-one basis such that a modulation vector #3 is mapped to a tile #0, a modulation vector #5 is mapped to a tile #1, a modulation vector #2 is mapped to a tile #2, a modulation vector #7 is mapped to a tile #3, a modulation vector #6 is mapped to a tile #4, and a modulation vector #4 is mapped to a tile #5.
A second step, after determining a modulation vector sequence that is mapped to the 6-bit CQI on an one-to-one basis, determines a QPSK sequence mapped to each of the modulation vectors constituting the modulation vector sequence.
That is, the second step determines QPSK sequences mapped to the modulation vectors on an one-to-one basis (i.e., each modulation vector is mapped to an individual QPSK sequence), and the QPSK sequences individually mapped to the modulation vectors are shown in Table 2.
TABLE 2Modulation vectorQPSK sequence0P0, P1, P2, P3, P0, P1, P2, P31P0, P3, P2, P1, P0, P3, P2, P12P0, P0, P1, P1, P2, P2, P3, P33P0, P0, P3, P3, P2, P2, P1, P14P0, P0, P0, P0, P0, P0, P0, P05P0, P2, P0, P2, P0, P2, P0, P26P0, P2, P0, P2, P2, P0, P2, P07P0, P2, P2, P0, P2, P0, P0, P2
As shown in Table 2, each modulation vector is mapped to a length=8 QPSK sequence on an one-to-one basis (i.e., each modulation vector is mapped to an individual QPSK sequence), and elements constituting the QPSK sequence are mapped to eight data sub-carriers of each of the tiles constituting a CQI channel on an one-to-one basis (i.e., each one of the QPSK sequence is mapped to an individual data sub-carrier). For example, if a modulation vector to be transmitted over a particular tile is modulation vector #0, eight data sub-carriers constituting the particular tile sequentially transmit P0, P1, P2, P3, P0, P1, P2, and P3, respectively. That is, if the particular tile is an mth tile of an nth CQI channel, Mn,8m among eight data sub-carriers constituting the mth tile transmits P0, Mm,8m+1 transmits P1, Mn,8m+2 transmits P2, and Mn,8m+3 transmits P3, Mn,8m+4 transmits P0, Mn,8m+5 transmits P1, Mn,8m+6 transmits P2, and Mn,8m+7 transmits P3, to thus map each one of the QPSK sequence to an individual data sub-carrier. The elements P0 through P3 constituting the QPSK sequence can be expressed as Equation (1) below, representing a constellation of a QPSK signal.
                                          P            ⁢                                                  ⁢            0                    =                      exp            ⁡                          (                              j                ·                                  π                  4                                            )                                      ⁢                                  ⁢                              P            ⁢                                                  ⁢            1                    =                      exp            ⁡                          (                              j                ·                                                      3                    ⁢                    π                                    4                                            )                                      ⁢                                  ⁢                              P            ⁢                                                  ⁢            2                    =                      exp            ⁡                          (                                                -                  j                                ·                                                      3                    ⁢                    π                                    4                                            )                                      ⁢                                  ⁢                              P            ⁢                                                  ⁢            3                    =                      exp            ⁡                          (                                                -                  j                                ·                                  π                  4                                            )                                                          (        1        )            
The modulation vector sequences and the QPSK sequences constituting each of the modulation vector sequences are predefined between the BS and the MS and transmission from the BS to the MS of information as to the modulation vector sequence is not necessary. As described above, the MS can transmit the QPSK signal generated through the two steps to the BS over a CQI channel, and the BS can receive the CQI channel signal transmitted by the MS and detect the CQI transmitted by the MS by performing correlation between the modulation vector sequences and the QPSK sequences constituting each of the modulation vector sequences.
However, the CQI transmission/reception scheme described above may not consider CQI reception performance of the communication system, the number of reception antennas of a receiver, an increase in gain of reception power of the receiver, and/or inefficient use/waste of CQI channel resources. Although the IEEE 802.16e communication system was discussed in detail above, the foregoing deficiencies may also arise in other communication systems including but not limited to CDMA and TDMA systems. Accordingly, there is a demand for an improved CQI communication scheme applicable in various communication systems.